High altitude ballooning is very exiting because you can gather really interesting data and images. Bu in order to make this flight successful you need not only a balloon, but also tracking device as well. Because balloon once fired, it can travel hundreds of kilometers until it reaches high altitudes and then explode. So you need to gear it up with find it when it falls down. Ugifer build his high altitude balloon tracker with Arduino core.
Obviously to locate balloon coordinates there is a GPS module used. Then comes a row of sensors including couple DS1820 temperature sensors, absolute pressure sensor. Data then is logged to SD card for later review. And finally Radiometrix NTX2 radio module for relatively long range data transfer which transmits balloon coordinates. The balloon traveled 38km up which is decent height but still not close to other records that reach 100km. Anyway this is more than enough to get exiting results.